In order for a computer to operate successfully, it is necessary to supply stable power to the computer. For a supply of the stable power to the computer, the uninterruptible power supply (UPS: Un-interruptible Power Supply) device has been used. The uninterruptible power supply device (hereinafter referred to as UPS) is provided with a battery as a backup power. For this reason, by switching the power supply to the battery, in the event of a power failure, it is possible to supply power to the computer.
In view of power saving, it is effective to cut the power supply to the computer from the UPS, when the computer does not require the power supply. Therefore, a method of indicating the power-off from the computer to the UPS has been proposed. For example, at the time of power-off, the computer software issues command to cut the UPS output after a few minutes (setting time), to the UPS. When the setting time elapses after receiving the command, the UPS cuts the power supply output unconditionally.
Within the designated time, the computer saves data, performs end processing of the application, and stops OS (Operating System). That is, because the computer is unable to control the UPS, after the OS is stopped, the setting time of the UPS was set to longer time with a margin.